manifest_check.py: trim namespace part of the module, if needed.

Normally Soong does that automatically when it handles module names
specified in Android.bp properties. However not all <uses-library>
entries in the manifest correspond to real modules: some of the
optional libraries may be missing at build time. Therefor this script
accepts raw module names as spelled in Android.bp/Amdroid.mk and trims
the optional namespace part manually.

Bug: 193891722
Test: manifest_check_test.py
Test: $ lunch aosp_cf_x86_64_phone-userdebug && m && launch_cvd
      $ adb wait-for-device && \
        adb root && \
        adb logcat | \
        grep -E 'ClassLoaderContext [a-z ]+ mismatch' -C1
      # empty output, no errors

Change-Id: I184fb8a2dc26f49e90fb597ebcd6a58c00705206